The invention relates generally to a system and method of operating a turbocharged engine and, more specifically, to a system and method for controlling compressor choke in a turbocharged engine operated at high altitude regions.
In certain applications, the turbocharged engines are used in relatively extreme environmental conditions, such as high altitudes. For example, diesel powered locomotives can travel through a wide range of environmental conditions, particularly in mountainous regions. These environmental conditions can adversely affect engine performance, efficiency, exhaust pollutants, and other engine characteristics. For example, diesel engines operating in mountainous regions are subject to greater loads due to higher gradients, lower atmospheric pressures due to higher altitudes, lower temperatures due to colder climate or higher altitude, lower air density due to lower atmospheric pressure, and so forth. At high altitudes, the compressor and the turbocharger speed can increase beyond a preselected limit without suitable control measures. In addition, the pressure ratio across the compressor can increase beyond a preselected limit at high altitudes, such that an operating point of the compressor is pushed into a choke region. The maximum compressor volume flow rate is often limited by the cross-section of a compressor inlet. For example, if the air flow rate at a compressor wheel inlet reaches a sonic velocity, then no further increase in the air flow rate is possible. This threshold limit in the air flow rate is represented as a “choke line”. In certain cases, the speed of the turbine may be maintained within the design limit by reducing the power output of the engine. However, reducing of the power output of the engine at higher altitudes results in reduction of hauling capacity of the engine.
Therefore, a technique is needed for controlling compressor choke in a turbocharged engine operated at high altitude regions.